Regardless of the distro you choose, as long as you don't install X you should be all right.
Not sure about slack, but RH and Mandy have hardware compatability lists at their websites, so you could see if your HW is supported there. (rule of thumb: if it works in one distro it will likely work with any..)
other than that, there is no reason why you cant give it a try and see if it don't work.
I used to have RH 8 installed on a 233, so I'm sure you can get something running on the old 100.